With the holidays quickly approaching, giving back is on all of our minds, which is why InStyle caught up with several stars for our “Shining Stars” story in the new December issue to see how they support the causes closest to their hearts. We’ve got behind the scenes video with two of the celebrities featured—Leighton Meester, who works with blood cancer-focused organization DKMS America (Vera Wang introduced her to their work!), and Colin Farrell about his work with the Foundation for Angelman Syndrome Therapeutics (his son suffers from the illness). “It’s just so simple to help,” Meester said. Watch the video above, and flip to page 447 of our December issue to get the full story—or download it on your iPad, Nook, or Droid tablet.